1. Field of the Invention
This invention relates to a solar heat collector having a cover plate mounted in spaced relation to a solar energy absorber.
2. Description of the Prior Art
The advantages of using solar heat collectors to collect solar energy for heating a fluid and/or for generating electric power have been recognized in the prior art. For example, advantages and embodiments of prior art solar heat collectors are discussed in (1) an article entitled "Solar Energy Researchers Try A New Way" Business Week, June 12, 1971, page 72; (2) an article entitled "Solar Energy: A Feasible Source of Power?", Science, Volume 172, page 660; and (3) U.S. Pat. No. 2,888,007.
In general, there is disclosed in the above-mentioned patent a window for admitting and trapping solar radiation including a cover plate, a receiver and a glass plate mounted in spaced, parallel relation in an insulated box.
The inner surface of the cover plate is ribbed to form a series of continuous, parallel, substantially cylindrical lenses which lenses focus the sun's rays on a focal plane in the box. The glass plate is disposed in the box between the cover plate and the receiver. The surface of the glass plate adjacent the receiver lies in the focal plane and is selectively coated with a mirror face to provide the surface with a number of slots equal to the number of lenses on the cover plate.
The solar energy passes through the slots and strikes the receiver surface. Solar energy that is not absorbed by the receiver is reflected from the receiver to the mirror face of the glass plate which, in turn, reflects the solar energy back toward the receiver.
The window as disclosed in the above-mentioned patent has disadvantages. For example, a portion of the energy not absorbed by the receiver escapes through the slots. Another disadvantage is that the window has to be built with precision. More particularly, the slots on the glass plate have to be as small as possible to prevent the reflected energy from the receiver from passing therethrough and the glass plate has to be positioned in the focal plane for maximum efficiency. A third drawback is that the window has to be rotated in coordination with the movement of the sun and/or the glass plate laterally displaced relative to the receiver so that the sun's rays, which travel in a straight line, impinge on the cover plate lenses and are concentrated at the focal plane. A fourth drawback is that the coating on the glass plate has been found to peel as the temperature of the window increases. When this occurs, the reflectance of the glass plate decreases and an increased amount of energy escapes from the window.
It would be advantageous, therefore, if a solar heat collector were provided that did not have the drawbacks of the prior art.